The equivalent of a substance is the mass which supplies or consumes one mole of another substance in a reaction. Equivalents can be used to simplify balancing chemical equations for many reactions. When using equivalents it is often not necessary to write balanced equations to find the amount of substances participating in the reaction. As a result, although to determine the equivalent weight of a substance you must specify the reactants and the products involved in a reaction, the equation does not have to be balanced. Because one equivalent always reacts with one equivalent, the use of equivalents can be of great help when trying to work with reactions where the balanced equation is not known.

In acid-base reactions the equivalent weight is the gram molecular weight of acid that yields an Avogadro number (6.022 x 10²³) of hydrogen ions (or, depending on the acid-base scheme, the mass required to...